Method and apparatus for controlling disc drive using counter-electromotive force

ABSTRACT

A method and an apparatus to control a disc drive, and more particularly, a method and an apparatus to control a disc drive using an indirectly determined counter-electromotive force. The method of controlling the disc drive using a counter-electromotive force includes determining a change in a servo parameter of the disc drive; and controlling the disc drive based on the determined change.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-part of application Ser. No.10/649,779, now U.S. Pat. No. 7,064,917. This application claims thepriority of Korean Patent Application No. 2002-51162, filed on Aug. 28,2002, in the Korean Intellectual Property Office, the disclosure ofwhich is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus to control adisc drive, and more particularly, to a method of controlling and anapparatus to control a disc drive using an indirectly determinedcounter-electromotive force, which prevents collision and malfunction ofa transducer and a disc by determining external vibrations and amagnitude of shock without installing an additional shock sensor in thedisc drive.

2. Description of the Related Art

A hard disc drive includes a plurality of magnetic transducers whichsense a magnetic field and magnetize a single rotating disc or each of aplurality of rotating discs to write and read information on and fromthe disc. In general, the information is formatted in a plurality ofsectors in circular tracks. There is a number of tracks across eachsurface of a disc. Tracks located above each other on the plurality ofrotating discs are grouped into cylinders. Therefore, each track is alsodefined by a cylinder.

In general, each of the transducers is integrated into a sliderincorporated into a head gimbal assembly (HGA). Each HGA is attached toan actuator arm. The actuator arm has a voice coil adjacent to a certainmagnetic assembly, together with a voice coil motor. In general, thehard disc drive includes a driving circuit which supplies current usedto excite the voice coil motor, and a controller. The excited voice coilmotor rotates the actuator arm and moves each of the transducers acrosssurfaces of the discs.

When the information is written or read, there is a feasibility that thehard disc drive performs a seek routine when each of the transducers ismoved from one cylinder to another cylinder. During the seek routine,the voice coil motor is excited by a current used to move each of thetransducers to a new position on the surface of a disc. Also, thecontroller executes a servo routine on which each of the transducers ismoved to an accurate position of a cylinder with respect to a center ofa track.

The hard disc drive is very sensitive to disturbance caused by externalshocks. As such, when the disturbance exceeds a tolerance range of thehard disc drive, a malfunction may occur, and when the disturbance issevere, a collision between a transducer and disc surface may occur suchthat the transducer or disc may be severely damaged.

A well-known technique of protecting a disc drive from disturbance isdisclosed in U.S. Pat. No. 6,236,527 titled “Disk Drive with ActuatorLoad/Unload Controller.”

As shown in FIG. 1, the disc drive disclosed in U.S. Pat. No. 6,236,527includes a shock sensor 140, a ramp 6 as a load/unload mechanism toload/unload a disc 1, A/D converters 130 b and 140 b which convert ananalog signal into a digital signal, an actuator velocity detectingcircuit 130 a, a CPU 100 which determines and executes commands, a VCMdriver 120 which drives an actuator, and a spindle driver 110 whichdrives a spindle motor 2 to rotate the disc 1. The disc drive alsoincludes the actuator 3 as a position tracking driving unit to write andread data on and from the disc 1, a head/slider 4 that writes data onthe disc 1 and reads data from the disc 1, and a VCM coil 5 which drivesthe actuator 3.

The head/slider 4 that writes and reads data on and from the disc 1 andthe VCM coil 5 are both mounted in the actuator 3. The VCM coil 5,together with a permanent magnet (not shown), constitutes a voice coilmotor (VCM). The VCM moves the actuator 3, and the spindle motor 2rotates the disc 1. When the head/slider 4 is unloaded, the ramp 6supports a head arm. The actuator 3, the VCM, and the ramp 6 constitutea load/unload mechanism that loads/unloads the head/slider 4 onto/fromthe disc 1. The spindle driver 110 drives the spindle motor 2 accordingto commands from the CPU 100.

A feature of the disc drive disclosed in the above U.S. Pat. No.6,236,527 is that after a shock signal input to the disc drive is sensedusing the shock sensor 140 during loading/unloading of the head/slider4, if the value of the sensed shock signal exceeds a threshold, drivingof the actuator 3 is stopped, and the head/slider 4 is unloaded byforced driving without control of velocity so that the disc drive isprotected from external shocks.

According to the above related art, an additional sensor should be addedto sense the magnitude of an outside shock, increasing costs of the discdrive. In addition, only in the loading/unloading mode is the disc driveprotected from the external shocks, but the disc drive cannot beprotected from smaller disturbance occurring in a high frequency regionduring the seek and track following modes.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide amethod and an apparatus to control a disc drive using acounter-electromotive force, in which a magnitude of an external shockapplied to the disc drive is determined from the counter-electromotiveforce by using a signal applied to a voice coil or a position errorsignal without an additional shock sensor. A servo mechanism of the discdrive is controlled according to the determined magnitude of theexternal shock.

It is another aspect of the present invention to indirectly determinethe counter-electromotive force through a change in servo parametervalues. The servo parameter values include the current (3-phase current)applied to a spindle motor, a torque and/or a rotational speed of thespindle motor, and a duty ratio of a pulse width modulation (PWM) forthe driving control of the spindle motor.

Additional aspects and advantages of the invention will be set forth inpart in the description which follows and, in part, will be obvious fromthe description, or may be learned by practice of the invention.

The foregoing and/or other aspects of the present invention are achievedby providing a method of controlling a disc drive using acounter-electromotive force. The method includes detecting a voltageapplied to a voice coil during a predetermined mode, performing anoperation of a value of the counter-electromotive force using thedetected voice coil voltage, comparing the value of thecounter-electromotive force operated with a predetermined threshold, andwhen the value of the counter-electromotive force is equal to or largerthan the predetermined threshold, controlling a voice coil motor and aspindle motor so that a current mode is stopped and a parking orunloading mode is executed.

The foregoing and/or other aspects of the present invention are achievedby providing a method of controlling a disc drive using acounter-electromotive force. The method includes detecting a movingdistance variation ΔLh/Δt of a transducer with respect to a variation intime during a predetermined mode, performing an operation of a value ofthe counter-electromotive force by applying the detected moving distancevariation ΔLh/Δt of the transducer with respect to the variation in timeto a predetermined counter-electromotive force calculation Equation,comparing the value of the counter-electromotive force with apredetermined threshold, and when the value of the counter-electromotiveforce is equal to or larger than the predetermined threshold,controlling a voice coil motor and a spindle motor so that a currentmode is stopped and a parking or unloading mode is executed.

The foregoing and/or other aspects of the present invention are achievedby providing a disc drive including a disc having a surface, a spindlemotor to rotate the disc, a transducer to write and read information inand from the disc, a voice coil motor to move the transducer, and acontroller to control the spindle motor and the voice coil motoraccording to a set mode, and to perform a shock damage preventionprocess of controlling the voice coil motor and the spindle motor, sothat a current mode is stopped and a parking or unloading mode isexecuted if a counter-electromotive force operation process ofperforming an operation of a value of a counter-electromotive forceusing a voltage detected from the voice coil and the value of thecounter-electromotive are equal to or larger than a predeterminedthreshold value.

The foregoing and/or other aspects of the present invention are alsoachieved by providing a method of controlling a disc drive using acounter-electromotive force, comprising determining a change in a servoparameter of the disc drive and controlling the disc drive based on thedetermined change.

The foregoing and/or other aspects of the present invention are achievedby providing a disc drive including a disc having a surface, a spindlemotor to rotate the disc, a transducer to write and read information inand from the disc, a voice coil motor to move the transducer, and acontroller to control the spindle motor and the voice coil motoraccording to a set mode, and using a moving distance variation ΔLh/Δt ofthe transducer with respect to a variation in time detected during theset mode Δt, to perform a shock damage prevention process of controllingthe voice coil motor and the spindle motor so that a current mode isstopped and a parking or unloading mode is executed if acounter-electromotive force operation process of performing an operationof the value of a counter-electromotive force using a predeterminedcounter-electromotive force calculation Equation and the value of thecounter-electromotive force of which operation is performed in thecounter-electromotive force operation process are equal to or largerthan a predetermined threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects and advantages of the invention willbecome apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 shows a structure of a conventional disc drive including a shocksensor;

FIG. 2 shows a top view of a disc drive, according to an embodiment ofthe present invention;

FIG. 3 shows a circuit diagram of an electrical system of controllingthe disc drive shown in FIG. 2;

FIG. 4 shows a flowchart illustrating a method of controlling the discdrive using a counter-electromotive force according to an embodiment ofthe present invention;

FIG. 5 shows a flowchart illustrating another method of controlling thedisc drive using the counter-electromotive force according to anembodiment of the present invention;

FIG. 6 shows a method of obtaining a counter-electromotive force from aposition error signal;

FIG. 7 shows a method of indirectly determining a shock amount based onservo parameters; and

FIGS. 8-11 illustrate the changes in the servo parameters of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings, wherein like reference numerals refer tothe like elements throughout. The embodiments are described below inorder to explain the present invention by referring to the figures.

FIG. 2 shows a top view of a disc drive, according to an embodiment ofthe present invention. A drive 10 includes at least one magnetic disc 12rotated by a spindle motor 14. The drive 10 further includes atransducer 16 adjacent to a disc surface 18.

The transducer 16 senses a magnetic field and magnetizes the disc 12 toread/write information from/on the rotating disc 12. In general, thetransducer 16 is coupled with the disc surface 18. Although a singletransducer 16 is shown, the transducer 16 includes a writing transducerto magnetize the disc 12 and a separated reading transducer to sense themagnetic field of the disc 12. The reading transducer includes amagneto-resistive (MR) device.

The transducer 16 may be integrated into a slider 20. The slider 20 isdesigned to generate an air bearing between the transducer 16 and thedisc surface 18. The slider 20 is coupled with a head gimbal assembly(HGA) 22. The HGA 22 is attached to an actuator arm 24 having a voicecoil 26. The voice coil 26 allows a voice coil motor (VCM) 30 to beadjacent to a magnetic assembly 28. Current flowing through the voicecoil 26 causes a torque used to rotate the actuator arm 24 with respectto a bearing assembly 32. The rotation of the actuator arm 24 causes thetransducer 16 to move across the disc surface 18.

Generally, information is stored in a circular track 34 of the disc 12and, each track 34 includes a plurality of sectors. Each of the sectorsincludes a data field and an identification field. The identificationfield includes a gray code used to identify a sector and a track (acylinder). The transducer 16 is moved across the disc surface 18 so asto read/write information from/on another track. Moving the transducer16 across another track is generally referred to as a seek routine.

FIG. 3 shows a circuit diagram of an electrical system of controllingthe disc drive shown in FIG. 2. An electrical system 40 includes aread/write (R/W) channel 44 and a controller 42 coupled with thetransducer 16 by a pre-amplifier 46. The controller 42 includes adigital signal processor (DSP), a microprocessor, and a microcontroller.The controller 42 applies a control signal to the R/W channel 44 so asto read and write information from and on the disc 12. Information istransmitted to a host interface 47 from the R/W channel 44. The hostinterface 47 includes a buffer memory to allow the disc drive and acontrol circuit to interface with a system, such as a personal computer(PC).

Also, the controller 42 is coupled with a VCM driver 48 which suppliesdriving current to the voice coil 26. The controller 42 applies acontrol signal to the VCM driver 48 to control excitation of the VCM 30and movement of the transducer 16.

In a read mode, the R/W channel 44 converts an analog signal read by thetransducer 16 and amplified by the pre-amplifier 46 into a digitalsignal that may be read by a host computer (not shown), outputs thedigital signal to the host interface 47, and receives user data outputfrom the host computer from the host interface 47. In a write mode, theR/W channel 44 converts the user data into a recording current which maybe written in the disc 12, and outputs the recording current to thepre-amplifier 46.

The controller 42 is also coupled with a read only memory (ROM) elementor a nonvolatile memory element, such as a flash memory element 50, anda random access memory element 52. The memory elements 50 and 52 includea command used by the controller 42 and data so as to execute a softwareroutine. The software routine includes the seek routine on which thetransducer 16 is moved from one track to another track. The seek routineincludes a servo control routine during which the transducer 16 is movedto a correct track.

Also, programs as described in the flowcharts illustrating a method ofcontrolling a disc drive using a counter-electromotive force as shown inFIGS. 4 and 5 of the present invention, are stored in the memoryelements 50 and 52.

In order to perform an operation of a counter-electromotive force usinga voice coil voltage, according to an embodiment of the presentinvention, a voltage detector 56, which detects the voice coil voltage,and an analog/digital (A/D) converter 58, which converts the detectedvoice coil voltage into a digital signal, are provided. The controller42 is designed to perform a shock damage prevention process bycontrolling the VCM 30 and the spindle motor 14 so that a current modeis stopped and a parking or unloading mode is executed if acounter-electromotive force operation process to perform an operation ofa value of the counter-electromotive force using the voltage detectedfrom the voice coil and the value of the counter-electromotive force, ofwhich operation is performed in the counter-electromotive forceoperation process, are equal to or larger than a predetermined thresholdvalue. Preferably, the voltage detector 56 is designed to include anamplifier and a filter to attenuate noise, because a signal detectedusing the counter-electromotive force is very small.

Next, in a method of detecting a counter-electromotive force using aservo signal according to another embodiment of the present invention,the voltage detector 56 and the analog/digital converter 58 are notneeded. Here, the controller 42 is designed to calculate ΔLh/Δt, whichis a moving distance variation ΔLh of the transducer with respect to avariation in time Δt, by analyzing the servo signal and to perform ashock damage prevention process of controlling the VCM 30 and thespindle motor 14, so that a current mode is stopped and a parking orunloading mode is executed if the counter-electromotive force operationprocess of performing an operation of the value of thecounter-electromotive force using a predetermined counter-electromotiveforce calculation Equation and the value of the counter-electromotiveforce of which operation is performed in the counter-electromotive forceoperation process are equal to or larger than a predetermined thresholdvalue.

Thus, the controller 42 calculates the counter-electromotive force usinga position error signal, which is a servo signal or a voice coilvoltage. If the calculated value of the counter-electromotive force isequal to or larger than a threshold level, the controller 42 determinesthat external shocks or vibrations exceed a tolerance range of a system,stops the current mode so as to protect the disc drive, and controls theservo mechanism to convert to a parking or unloading mode.

In addition, a delay time may occur between a driving signal output fromthe VCM driver 48 and a signal detected from the voice coil 26. Thus, inorder to calculate correct counter-electromotive force, it is effectivethat a circuit to compensate for signal delay between the driving signaland a voltage detection signal from the voice coil 26 is installed inthe controller 42.

Hereinafter, a method of controlling a disc drive using acounter-electromotive force according to the present invention will bedescribed in detail.

First, a principle of the counter-electromotive force generated in thevoice coil by disturbance is as follows. When disturbance, such as anexternal vibration or an external shock, occurs when a transducer readsor writes a signal along a certain track, the HGA 22 makes a smallmovement in a horizontal direction such that the voice coil 26 moves onthe voice coil motor 30 in which a magnetic force is uniformlydistributed. In this case, the voice coil 26 makes a fine vibration in auniform magnetic force, thereby generating the counter-electromotiveforce.

A method of obtaining the counter-electromotive force includes using avoice coil voltage and using a position error signal.

First, a method of controlling a disc drive using acounter-electromotive force according to the embodiment of the presentinvention using a voice coil voltage will be described with reference tothe flowchart of FIG. 4.

In operation 410, the controller 42 determines commands input to thehost interface 47 and executes a corresponding mode. As an example, thecontroller 42 executes a loading mode, a seek mode, a track followingmode, a read mode, and a write mode according to the commands.

In operation 420, a voltage is detected from the voice coil 26 while acurrent mode is executed. In operation 430, the detected analog voicecoil voltage is converted into a digital signal.

However, a delay time may occur between a driving signal output from theVCM driver 48 and a signal detected from the voice coil 26. Thus, inorder to calculate a correct counter-electromotive force, in operation440, the delay between the driving signal and the voltage detectionsignal of the voice coil 26 is compensated by a delay circuit (notshown) installed in the controller 42.

In operation 450, a counter-electromotive force e(t) of the voice coil26 is obtained by Equation 1.

$\begin{matrix}{{e(t)} = {{v(t)} - {L \times \left( \frac{\mathbb{d}i}{\mathbb{d}t} \right)} - {R \times {i(t)}}}} & (1)\end{matrix}$

Here, v(t) is a voltage detected from a voice coil, L is a reactanceconstant of the voice coil, R is a resistance toward the voice coil fromthe VCM driver, and i is current applied to the voice coil.

Next, in operation 460, the value of the counter-electromotive force ofwhich the operation is performed in operation 450 is compared with athreshold Vth. Here, the threshold Vth is statistically determined by amaximum magnitude of a shock or the magnitude of vibration within atolerance range of the system, according to a correlation between thecounter-electromotive force and the magnitude of shock throughexperiments. That is, the threshold Vth is obtained from a regressionfunction defined between an external shock or the magnitude of vibrationand a voice coil counter-electromotive force from the correlation.

When the value of the operated counter-electromotive force is smallerthan the threshold Vth as a result of comparison in operation 460, thiscase corresponds to the magnitude of shock or the magnitude of vibrationwithin a tolerance range of the disc drive. Thus, a current mode isnormally executed, returns to operation 420, an operation is iterativelyperformed on the value of the counter-electromotive force, and then thevalue of the counter-electromotive force is compared with the thresholdVth.

If the value of the operated counter-electromotive force is equal to orlarger than the threshold Vth as a result of comparison in operation460, the magnitude of an external shock or the magnitude of shockdetermined by the value of the operated counter-electromotive forceexceeds the tolerance range of the disc drive. Thus, in operation 470,in order to prevent damages of the transducer and the disc due tocollision with the transducer and the disc, a shock damage preventionprocess of controlling the VCM and the spindle motor is performed sothat the current mode is stopped and a parking or unloading mode isexecuted. This is because it takes a predetermined time for disturbanceto spread. Thus, the disturbance is prevented from being transferred tothe transducer and the disc and from making a bad effect on the functionof the disc drive.

Next, the method of controlling a disc drive using acounter-electromotive force according to the embodiment of the presentinvention using a position error signal will be described with referenceto the flowchart in FIG. 5.

In this embodiment, the counter-electromotive force signal of the voicecoil 26 is obtained using a variation in rotational speed of thetransducer 16 based on a counter-electromotive constant Ke of the voicecoil 26 determined in a design operation and the position error signalgenerated from the servo signal read by the transducer 16. In thismethod, the HGA 22 is assumed to be a rigid body. However, thetransducer 16 is attached to a suspension, and the transducer 16 and thesuspension are attached to the bearing assembly 32 such that thestructure of the disc drive is more sensitive to disturbance and themethod may be used even in a disturbance occurring in a high frequencyregion.

In operation 510, the controller 42 determines commands input to thehost interface 47 and executes a corresponding mode. As an example, thecontroller 42 executes a loading mode, a seek mode, a track followingmode, a read mode, and a write mode according to the commands.

In operation 520, the controller 42 detects ΔLh/Δt, which is a movingdistance variation ΔLh of the transducer with respect to a variation intime Δt, using the position error signal as the servo signal when thetransducer is moved from a track b to a track a as shown in FIG. 6.

In operation 530, a counter-electromotive force e(t) of the voice coil26 is obtained by Equation 2.

$\begin{matrix}{{e(t)} = {\left( \frac{Ke}{Rh} \right) \times \left( \frac{\mathbb{d}{Lh}}{\mathbb{d}t} \right)}} & (2)\end{matrix}$

Here, Ke is a counter-electromotive force constant, and Rh is a distancefrom a pivot bearing to the transducer 16, as shown in FIG. 6.

In operation 540, the value of the counter-electromotive force of whichoperation is performed in operation 530 is compared with a thresholdVth. Here, the threshold Vth is statistically determined by a maximummagnitude of a shock or the magnitude of vibration within a tolerancerange of the system, according to a correlation between thecounter-electromotive force and the magnitude of shock throughexperiments. That is, the threshold Vth is obtained from a regressionfunction defined between an external shock or the magnitude of vibrationand a voice coil counter-electromotive force from the correlation.

When the value of the operated counter-electromotive force is smallerthan the threshold Vth as a result of comparison in operation 540, thiscase corresponds to the magnitude of shock or the magnitude of vibrationwithin a tolerance range of the disc drive. Thus, a current mode isnormally executed, returns to operation 520, an operation is iterativelyperformed on the value of the counter-electromotive force, and then thevalue of the counter-electromotive force is compared with the thresholdVth.

If the value of the operated counter-electromotive force is equal to orlarger than the threshold Vth as the result of comparison in operation540, the magnitude of an external shock or the magnitude of shockdetermined by the value of the operated counter-electromotive forceexceeds the tolerance range of the disc drive. Thus, in operation 550,in order to prevent damages of the transducer and the disc due tocollision with the transducer and the disc, a shock damage preventionprocess of controlling the VCM and the spindle motor is performed sothat the current mode is stopped and a parking or unloading mode isexecuted.

The counter-electromotive force of which operation is performed usingthe voice coil voltage and the position error signal, may be detectedeven in a large disturbance occurring in a low frequency region and evenin a smaller disturbance occurring in a high frequency region.

Likewise, a counter-electromotive force is calculated using a voice coilvoltage or a position error signal as a servo signal without installingan additional shock sensor in a disc drive, and the magnitude of anexternal shock or the magnitude of vibration is determined by thecalculated counter-electromotive force. When the magnitude of anexternal shock or the magnitude of vibration determined by thecounter-electromotive force exceeds a tolerance range of the disc drive,a current mode is automatically converted into a parking or unloadingmode, and damage due to a collision between the transducer and the discmay be prevented.

A third embodiment of the present invention is illustrated in FIGS.7-11. The counter-electromotive force can be indirectly determinedthrough a change in servo parameter values of the spindle motor 14. Theservo parameters include the current (3-phase current) applied to thespindle motor 14 from a spindle driver 54, the torque and/or therotational speed of the spindle motor 14, and the duty ratio of pulsewidth modulation (PWM) for the driving control of the spindle motor 14from the controller 42 to the spindle driver 54.

Referring to FIGS. 8-11, when an external interference is applied to thedisc drive 10, these servo parameters are changed instantly andindependently. As shown in FIG. 7, to use this characteristic todetermine the counter-electromotive force, the changes in the servoparameter values are experimentally determined as a function of theamount of shock during a design step (600). Servo parameter criticalvalues corresponding to the critical shock amount that is tolerable bythe disc drive 10 are determined and stored in a memory (610). Thecontroller 42 then monitors the changes in the servo parameter valuesduring the operation of the disc drive 10 (620). The controller 42compares the servo parameter values during operation with the servoparameter critical values to determine whether the operational servoparameter values exceed the servo parameter critical values (630),thereby indirectly detecting the shock amount. If the shock amount istoo great, the controller stops the current mode and controls the servomechanism to convert to a parking or unloading mode (640).

As described above, according to the present invention, acounter-electromotive force is calculated using a voice coil voltage ora position error signal as a servo signal without installing anadditional sensor to sense disturbance in a disc drive. In addition, themagnitude of an external shock or the magnitude of vibration areindirectly determined by the calculated counter-electromotive force orthe changes in servo parameters, and the disc drive is therebycontrolled such that malfunction due to a disturbance and damage due toa collision between a transducer and a disc are prevented. Further, asensor to sense a disturbance is not needed such that costs are reducedcompared to the related art. Further, disturbance is measured by thecounter-electromotive force even during a track following mode movedwith small displacement such that the disc drive is prevented from asmall disturbance even while the track following and read/write mode areexecuted.

The present invention may be implemented by a method, an apparatus, anda system. When the present invention is implemented with a softwareunit, elements of the present invention are code segments to performessential works. Programs or code segments may be stored in a processorreadable medium or transmitted in response to computer data signalscoupled with a carrier wave in a transmission medium or communicationnetworks. The processor readable medium includes a certain medium onwhich information may be stored or transmitted. The processor readablemedium includes an electronic circuit, a semiconductor memory device, aROM, a flash memory, an erasable ROM, a floppy disc, an optical disc, ahard disc, an optical fiber medium, and a radio frequency (RF) network.The computer data signals include certain signals which may betransmitted on a transmission medium, such as electronic networkchannels, optical fibers, airs, electronic fields, and RF networks.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A method of controlling a disc drive using a counter-electromotiveforce, comprising: determining a critical value of a change in a servoparameter value corresponding to a critical shock amount; measuring thechange in the servo parameter value during operation of the disc drive;determining whether the measured change in the servo parameter value isgreater than the critical value; and controlling the disc drive based onthe determined change wherein the servo parameter value comprises atleast a torque of the spindle motor, or a duty ratio of a pulse widthmodulation for driving control of the spindle motor.
 2. The method asclaimed in claim 1, wherein the controlling the disc drive comprisescontrolling a voice coil motor and a spindle motor of the disc drive sothat a current mode is stopped and a parking or unloading mode isexecuted if determined that the measured change in the servo parametervalue is greater than the critical value.